Abstract
The paper presents the experimental results and the results of direct numerical simulation of the development and interaction of two wave trains from two point sources of controlled disturbances in a supersonic boundary layer on a flat plate with an incident flow Mach number of 2.5. Sources were located parallel to the leading edge of the model. For the introduction of controlled disturbances into the boundary layer, the normal component of the mass flow rate was varied in the calculations. In the experiment, periodic glow discharges at a frequency of 20 kHz were used. In both cases, the disturbances sources worked synchronously. Mass flow rate pulsations were measured and recorded in sections, parallel to the leading edge of the model, near the maximum of disturbances along the boundary layer. In the experiment, a constant-temperature hot-wire anemometer was used. After performing a discrete Fourier transform, the spatial distributions of disturbances, the beta-spectra were determined, and the wave characteristics of the development of disturbances downstream were estimated. In addition, direct numerical simulation of the downstream development of disturbances from a single source was performed. The work presents a comparison of experimental and theoretical calculated data. The paper discusses the effects inherent in the interaction of unstable traveling controlled disturbances from two sources operating synchronously.
Highlights
Laminar-turbulent transition in the boundary layers is one of the fundamental problems in fluid dynamics, which has great practical significance
In a subsonic boundary layer, an oblique transition is initiated by a nonlinear interaction of two oblique waves of finite amplitude, symmetrical with respect to the flow direction
In the case of two sources of disturbances operating synchronously, the calculations revealed the effect of the interaction of two wave trains, which resulted in the formation of a characteristic interference pattern in the β-spectrum with a set of several nodes and antinodes
Summary
Laminar-turbulent transition in the boundary layers is one of the fundamental problems in fluid dynamics, which has great practical significance. To predict the laminar-turbulent transition, it is necessary to understand the dominant processes and their mechanisms responsible for the breakdown of the laminar regime We note here such nonlinear mechanisms of (2019) 1:14 interaction of disturbances as an oblique transition and subharmonic resonance [7, 8]. In a subsonic boundary layer, an oblique transition is initiated by a nonlinear interaction of two oblique waves of finite amplitude, symmetrical with respect to the flow direction. The effectiveness of such a path of turbulization is shown by the results of computational and experimental studies of the laminar – turbulent transition in the channel and in the boundary layer [9,10,11,12]. In the final stage of the transition, on longitudinal structures secondary unsteady disturbances (secondary high-frequency instability) develop, that eventually leads to the establishment of a turbulent regime
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